MRI-based attenuation correction for PET/MRI: a novel approach combining pattern recognition and atlas registration.
For quantitative PET information, correction of tissue photon attenuation is mandatory. Generally in conventional PET, the attenuation map is obtained from a transmission scan, which uses a rotating radionuclide source, or from the CT scan in a combined PET/CT scanner. In the case of PET/MRI scanners currently under development, insufficient space for the rotating source exists; the attenuation map can be calculated from the MR image instead. This task is challenging because MR intensities correlate with proton densities and tissue-relaxation properties, rather than with attenuation-related mass density.


METHODS
We used a combination of local pattern recognition and atlas registration, which captures global variation of anatomy, to predict pseudo-CT images from a given MR image. These pseudo-CT images were then used for attenuation correction, as the process would be performed in a PET/CT scanner.


RESULTS
For human brain scans, we show on a database of 17 MR/CT image pairs that our method reliably enables estimation of a pseudo-CT image from the MR image alone. On additional datasets of MRI/PET/CT triplets of human brain scans, we compare MRI-based attenuation correction with CT-based correction. Our approach enables PET quantification with a mean error of 3.2% for predefined regions of interest, which we found to be clinically not significant. However, our method is not specific to brain imaging, and we show promising initial results on 1 whole-body animal dataset.


CONCLUSIONS
This method allows reliable MRI-based attenuation correction for human brain scans. Further work is necessary to validate the method for whole-body imaging.
Hofmann
Matthias
M
Laboratory for Preclinical Imaging and Imaging Technology of the Werner Siemens-Foundation, Department of Radiology, Eberhard-Karls-University, Tuebingen, Germany.
Steinke
Florian
F
Scheel
Verena
V
Charpiat
Guillaume
G
Farquhar
Jason
J
Aschoff
Philip
P
Brady
Michael
M
Schölkopf
Bernhard
B
Pichler
Bernd J
BJ
D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging*; D016208:Databases, Factual; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010363:Pattern Recognition, Automated / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging